The natural gas hydrate is a future clean energy mainly consisting of methane and water, which is widely distributed in the Eastern and Western Pacific Ocean and at the western margin of the Atlantic Ocean. Its giant reserves and less pollution after combustion attracted attention of specialists in various countries in the energy field. Since marine exploitation is much more difficult than land exploitation, plenty of natural gas hydrate is still stored in the seabed and the permafrost up to now.
Risks exist with exploitation of the natural gas hydrate. Once blowout accident occurs, it might cause disasters such as tsunami, submarine landslide, seawater poisoning and the like. In addition, the presence of the natural gas hydrate might cause the seabed to be unstable, leading to large-scale submarine mudflow and causing severe damage to submarine pipeline and communication cables. If the submarine layer is broken in an earthquake, the gas generated by decomposition of the natural gas hydrate is ejected out of the sea surface, or a large amount of inflammable bubbles is formed on the seawater surface layer, which poses threat to the passing ships or even low-altitude flying airplanes. Therefore, during exploiting the natural gas hydrate, risk accidents should be prudently avoided.
Currently, three methods for exploiting the natural gas hydrate have been proposed: heat-injection, pressure-reduction and displacement processes. The heat-injection process includes decomposing methane steam in a heat injection manner by using the thermolabile characteristic of the natural gas hydrate. The pressure-reduction process uses the labile characteristic of the natural gas hydrate during depressurization. However, since the porous media in the submarine are not concentrated but evenly distributed, the decomposed natural gas is not easy to be collected, and how to arrange the pipelines and efficiently collect are problems to be solved in the art. The displacement method normally uses CO2 gas. As the ability of CO2 for forming the hydrate is stronger than CH4, under massive injection, it is possible to displace CH4 in the natural gas hydrate to reach the aim of exploitation. How to set reasonable temperature and pressure parameter range in the exploitation to avoid accident occurrence is the problem to be solved in the actual production.
Targeting to the above-mentioned situation, it is necessary to design a set of methods capable of simulating drilling and exploiting the hydrate layer indoors, and an apparatus for monitoring and analyzing the stratum parameter in the exploitation to optimize the exploitation method of natural gas hydrate under different environments, thereby predicting and evaluating the problem and risk in the actual production.